Nanoscale assembly of amyloid oligomers at physiologically relevant conditions

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Assembly of nanoaggregates by amyloid beta (Ab), as a widely accepted model for development of Alzheimer’s disease (AD), has recently gained additional support. The vast majority of in vitro studies are performed at Ab concentrations several orders higher than the physiologically relevant concentrations of Aβ in the brain; no nanoscale assembly of Aβ is observed at the low nanomolar concentration found in vivo. This suggests that the assembly of Aβ in vivo utilizes pathways different from those used in vitro. We discovered that spontaneous assembly of Aβ42 oligomers from monomers, within the physiological concentration range, can occur by utilizing the on-surface aggregation mechanism. Here, the surface acts as a catalyst for the aggregation process. We developed a model that explains the surface catalytic effect of the amyloid aggregation from monomers, at low nanomolar concentrations. In the model, the membrane effectively catalyzes amyloid aggregation by stabilizing aggregation-prone conformations. According to our preliminary data, this process depends on the membrane composition; therefore, we hypothesize that the change of the membrane composition is the factor that defines the assembly of the disease-prone Aβ aggregates. This hypothesis is supported by findings that aging is associated with changes in lipid composition and alterations of fatty acids at the level of lipid rafts were found in the early stage of AD. A thorough testing of this hypothesis is the major goal of this application. The rationale is that understanding the fundamental mechanisms of membrane-mediated Aβ nanoscale assembly will guide the development of practical approaches to control the aggregation process. The objective of this proposal is to characterize the on-surface formation of Aβ nanoscale assemblies, identify the aggregation-prone composition of cellular membranes, and develop a quantitative molecular model for future use in translational studies. Guided by strong preliminary data, we will test our central hypothesis through the following three specific aims: Aim 1: Characterize the nanoscale assembly processes of Ab monomers catalyzed by cellular membranes with different lipid compositions. Aim 2: Evaluate contributions of free lipids on the membrane catalysis of amyloid nanoassembly. Aim 3: Develop a molecular model for the membrane catalysis phenomenon using multi-scale theoretical and computational approaches. Aim 1 is focused on testing our hypothesis that the lipid composition of the membrane bilayer is the defining factor in spontaneous aggregation of Ab proteins at physiological concentrations. Under Aim 2, we will test the hypothesis that free lipids contribute further to the membrane catalysis of amyloid aggregation. Aim 3 proposes the use of various theoretical approaches and computer modeling to gain structural insights into the molecular mechanism of aggregation by the cellular membrane. The predictions of the theory will be tested under Aims 1 and 2. The proposed research plan, combining experimental studies with extensive computational modeling, will provide a molecular model for the Aβ nanoassembly process catalyzed by membranes at physiological concentrations of monomers. The development of preventative measures for the interaction of monomeric amyloids with membranes can help to control the aggregation process. This is a paradigm shift, which opens prospects for the development of new efficient treatments, early diagnostics, and preventive therapies for AD.